Manual Radiator Fan Control for Drag Racing

*Jime* · 06-17-2002, 02:08 PM

I wanted to have manual control over the radiator fan so that I could run the fan manually, without the car or the ignition switch being on. I have always liked the way the VW's fan runs after you shut the car off to cool the engine down, but wanted to be able to control it myself so that when racing I could manually turn the fan on and leave it on while waiting in the lineup for the next pass.

This switch allows just that, manual control while the car is off in one position and normal operation in the other position.
You have to a DPDT (double pole, double throw) switch. DO NOT get one with center off.

The relay is located just in front of the battery. You will see them labelled Cooling Fan Relay 1, 2 & 3. We are only going to connect into Cooling Fan Relay 1, it is located in the lower right corner.

Remove the two screws holding the relay, remove the top cover and then the bottom cover so you have access to the wires beneath the relays. Turn it over and look for the wires under Cooling Fan Relay 1. You will see two small gauge wires (these are the control for the relay) and two larger wires. (these are connected directly to the fan motors)

The only two wires we are interested in are the G/Y (Green with yellow stripe) and the LG/R (Light green with red stripe). Cut both of these wire leaving enough wire on each end to strip and connect into. (Indicated by the white X on the picture)

Connect four lengths of wire (for each of the cut ends) approximately 6' in length (to reach inside the car). I soldered mine but you can just strip and wrap the wires together or use a connector. Make sure you label them so you can tell them apart when they are inside the cockpit. I used 18 gauge wire, this is only signal wire for the relay it does not power the fans. Probably could be even smaller but I like to err on the side of caution.

I used red wire for the G/Y connections and green wire for the LG/R connections. I put black tape around the two wires that came from the relay for identification (they connect to the center terminals of the switch). I used the grommet just above the fuel filter to get into the car.
Once inside the car just hook them up to the switch as shown in the picture.

The other two connections on the switch go to a +12 hot wire and the other to ground. I used the +12 wire going to the hazard switch and tapped into it.

I have my switch so that down is normal operation and up turns on the fans manually.

It sounds a lot more difficult than it is, the whole operation should take a maximum of one hour most of which is deciding where to come through the firewall and where to mount the switch.

It could also be wired for high speed operation but I decided that the normal speed was sufficient for my needs.

*ejj* · 06-17-2002, 02:20 PM

Great writeup. I've been meaning to do this for a while, and just never got around to it. Have you tired it yet? Do you notice a drop it temps between runs?

*Jime* · 06-17-2002, 02:27 PM

Quote:

Originally posted by ejj5875
Great writeup. I've been meaning to do this for a while, and just never got around to it. Have you tired it yet? Do you notice a drop it temps between runs?

I have tried it, but not at the track. Pretty hard to tell how much it reduces temp because the gauge on the Max seems to stay in the same position (just below half) all the time. It sure blows hot air though so I am sure it is helping. Not sure how much circulation is going on once the thermostat closes though. It will circulate naturally with the pump off as long as the thermostat is open.

I am going to try it this weekend, its our second import race of the season.
http://www.importsociety.com/

They actually have a picture of my car (doing a VERY weak burnout) in the second page of the pictures from the 26 May event.

*MardiGrasMax* · 06-17-2002, 03:13 PM

I have had mine wired with an underhood switch for a while. It seems to work very well. I leave it running all the time when at the track. If you pop your hood in the staging lanes it works even better.

JAIMECBR900 · 06-17-2002, 10:01 PM

Thank you Jime. I'm going to try and do this before this weekend. I'm trying to make it back to the track on fri. night.

I vote they make this writeup a sticky.

njmaxseltd · 06-18-2002, 07:25 AM

I think I read somewhere on here that you can accomplish the same thing by taking the A/C compressor fuse out and turning the A/C on. The compressor will not run, but the cooling fans come on. After your done at the track, put the fuse back in and your all set.

I think thats a bit easier then wiring up a relay or a switch.

*Jime* · 06-18-2002, 09:59 AM

Quote:

Originally posted by njmaxseltd
I think I read somewhere on here that you can accomplish the same thing by taking the A/C compressor fuse out and turning the A/C on. The compressor will not run, but the cooling fans come on. After your done at the track, put the fuse back in and your all set.

I think thats a bit easier then wiring up a relay or a switch.

I tried that, only one LITTLE problem, it doesn't work unless the car is running. If your car is running you are just keeping it hot so it defeats the whole purpose of the cooling fans.

BBaker025 · 06-18-2002, 10:02 AM

GrEaT wRiTe Up MaN!

JAIMECBR900 · 06-18-2002, 10:17 AM

Quote:

Originally posted by Jime

I tried that, only one LITTLE problem, it doesn't work unless the car is running. If your car is running you are just keeping it hot so it defeats the whole purpose of the cooling fans.

Does the car have to be running or just the key on? Cause it would be the same with just the key on.

*Jime* · 06-18-2002, 10:20 AM

Quote:

Originally posted by JAIMECBR900

Does the car have to be running or just the key on? Cause it would be the same with just the key on.

Car has to be running for the fuse thing to work. Actually you have to pull the relay. Its a good idea for when you are driving back on the return road etc, just doesn't work unless car is running. Believe me I tried all the tricks I could before resorting to adding a switch. I even started a thread asking if anyone had done it.

*xHypex* · 06-18-2002, 07:00 PM

That was a nice write-up Jime

I wired mine up today, but I used wiretaps instead of cutting the wires. I would have soldered, but the fit was kinda tight. By using wiretaps you can also use a SPDT instead of a DPDT switch (or buy a DPDT and only use one set of the connectors). I also placed the switch inside the relay box so that I didn't have to run wires all the way inside the car. Then I can just flip the switch before getting back in the car.
Either way I had never thought of this mod before your post so thanks for the idea

-hype

*mzmtg* · 06-18-2002, 08:11 PM

Quote:

Originally posted by JAIMECBR900

I vote they make this writeup a sticky.

I added it to the FAQ.

Awesome write up!

*Jime* · 06-18-2002, 08:55 PM

Quote:

Originally posted by xHypex
That was a nice write-up Jime I wired mine up today, but I used wiretaps instead of cutting the wires. I would have soldered, but the fit was kinda tight. By using wiretaps you can also use a SPDT instead of a DPDT switch (or buy a DPDT and only use one set of the connectors). I also placed the switch inside the relay box so that I didn't have to run wires all the way inside the car. Then I can just flip the switch before getting back in the car.
Either way I had never thought of this mod before your post so thanks for the idea
-hype

I was going with the SPDT originally and not cut the wires but didn't want to take a chance of messing up the ECM so decided to isolate from it completely.
The switch I wanted in the car because I want to turn it on at the end of the run and have it cooling while coming back the return lane. Some days our run offs come pretty close together so want to get as much cooling as possible.

Toolrocks · 06-30-2002, 10:04 AM

A friend pointed me to this thread - great write up. I may do this as well. I was just gonna add that the few times I've raced my car at the track I run my heater on full blast too. Thinking that it will help remove heat from the cooling system and therefor, the engine.

*Jime* · 06-30-2002, 10:16 AM

Quote:

Originally posted by Toolrocks
A friend pointed me to this thread - great write up. I may do this as wee. I was just gonna add that the few times I've raced my car at the track I run my heater on full blast too. Thinking that it will help remove heat from the cooling system and therefor, the engine.

100% correct, not having the A/C on at the track makes it hot but the heater is #$%&*. However it does work. I know one guy who puts the heater on to warm up his bottle, the line is long enough to leave it connected and still watch the gauge. When it gets up to temp he just puts it back in the holder.

PS Also watch how long you leave the fans on for, I left mine on for about 45 mins and forgot about them and drained the battery. I also was running the bottle heater so pretty large drain. Felt sort of stupid getting a boost in the staging lanes.

*xHypex* · 06-30-2002, 11:23 AM

Quote:

Originally posted by Jime

PS Also watch how long you leave the fans on for, I left mine on for about 45 mins and forgot about them and drained the battery. I also was running the bottle heater so pretty large drain. Felt sort of stupid getting a boost in the staging lanes.

Jime does your fuel pump start when you turn on your fans? Mine does and some of the lights on the gauge cluster also turn on. It's not a big deal, but I try to be careful not to dump too much fuel into the engine on startup.
I haven't run the fans at the track yet, but would you say anything over ~30 mins without running the car would drain the battery a good deal? I guess I'll just see how it works and if it's worth it, and if I kill my battery I can always do a push start

-hype

*Jime* · 06-30-2002, 11:32 AM

Quote:

Originally posted by xHypex

Jime does your fuel pump start when you turn on your fans? Mine does and some of the lights on the gauge cluster also turn on. It's not a big deal, but I try to be careful not to dump too much fuel into the engine on startup.
I haven't run the fans at the track yet, but would you say anything over ~30 mins without running the car would drain the battery a good deal? I guess I'll just see how it works and if it's worth it, and if I kill my battery I can always do a push start
-hype

Nothing should come on but the fans if you hooked it up like my diagram. It must be where you got your +12V from. I took mine from the flasher plug +12V but you could take it from the lighter etc. The lighter would only allow the fans to start when the ignition switch is on accessories.
Gotta be something funny in your hookup, there is nothing that should make the fuel pump or gauge lights come on.

Check out you wiring again.
Jim

*xHypex* · 06-30-2002, 11:56 AM

I tapped my 12v from a wire that already runs from my battery (it used to run to my old fogs), so that shouldn't affect anything. I used the same two wires in your diagram, but I didn't cut them; I only tapped into them. Either way I hardly use the fans so it's not a big deal. I probably won't bother rewiring it, but the idea was still a good one

-hype

Toolrocks · 06-30-2002, 08:09 PM

Quote:

Originally posted by xHypex
I tapped my 12v from a wire that already runs from my battery (it used to run to my old fogs), so that shouldn't affect anything. I used the same two wires in your diagram, but I didn't cut them; I only tapped into them. Either way I hardly use the fans so it's not a big deal. I probably won't bother rewiring it, but the idea was still a good one
-hype

Since you didn't cut the wires or diode isolate them, you're sending 12 volts back to anything else that gets powered by that circuit. That could possibly be a bad thing. Not sure though. I know it's a pain to redo something but I'd probably re-wire it. Good luck.

*phatmax95* · 07-28-2002, 08:23 PM

I have a few questions regarding the writeup.

How will I know the switch is a DPDT?
Can I use a regular switch and wire it differently?

I cut the two wires and add a 6' section to each end, correct?

From what I gather, the switch has 4 connections.
1 comes from the +12
1 comes from the ground
1 comes from the LG/R wire closest to the relay
1 comes from the G/Y wire closest to the relay

Now, the other two wires that are loose (the wires farthest from the relay that were cut)... Where do they go?

They look like they both tie into the G/Y wire? I dont know so help me on that part.

Also, can I just connect the +12 and ground wire straight from the battery to the switch, or from the battery to a grounded screw? ( and not the hazards or whatever he did?)

Thanks alot..

Toolrocks · 07-28-2002, 09:56 PM

Buy a switch that says it is DPDT (it will be on the packaging, or have the person at the store help you)
You could use a regular switch but that would complicate things tremendously - you'd need to wire in a relay or diode isolate blah, blah, blah
Just buy the recommended switch and wire it up exactly as the diagram shows. There is a total of 6 connections. A DPTH swich will have 6 posts on the back of it. These posts are in two groups of 3. In each of the 3 post groups there is 1 post that is connected to another post, in that group, when the switch is in one posistion. When you flip the switch into the other position, the post will then "switch" from the post it was connected to, to the other post within that 3 post group. I hope that makes some sense.

Refer to the picture on the first thread.

So the wiring would actually be:
1> +12 Volts
2> Ground
3> G/Y to the switch
4> G/Y to the switch (yes another wire)
5> LG/R to the switch
6> LG/R to the switch (hope you got it by now)

Hope this helps. Good luck.
Yes, you could directly hook it up to the battery but, make sure you put a fuse in that line close to the battery.

*phatmax95* · 07-29-2002, 07:28 PM

Well. I wired it all up and it works great.. great idea too, btw. If I had known that the switch had 6 posts, then I would have understood the picture. And about that fuse near the battery.. is that just to protect the switch? If I do get one, which rating should it be? Thanks again.

Toolrocks · 07-29-2002, 10:56 PM

Glad to hear it is working for you. Fuses are primarily used to protect the power source and circuit from further damage. If the wire from the battery to the switch were to get grounded, it would possibly discharge your battery completely or, more likely, burn the insulation off the wire the entire length back to the battery and ignite anything else it may be touching. You can use a simple in-line 10amp fuse. That is the rating of the fuse used to protect the factory circuit, so use that. Good luck.

*phatmax95* · 07-29-2002, 11:07 PM

Thanks for all your help. I'll run out tomorrow and buy a fuse to throw on there.

*Jime* · 10-13-2003, 07:14 PM

I revised this mod in the spring when I got the 95 but just never got around to posting it. Aaron was kicking my butt this weekend so I though I would post it.

All that is necessary is to ground pin #13 of the ECU for High Speed and pin #14 for low speed. Just connect to the wire by soldering etc, it is not necessary to cut, you must leave the original circuit connected.

You can do either one or both. You will need just a simple on-off (spst single pole single throw) switch for one and an on-off-on (spdt single pole double throw) for both.

Almost any switch size can be used it is signal only, no current. All the ECU